Many applications in the field of analytical research and clinical testing utilize methods for analyzing liquid samples. Among those methods are optical measurements that measure absorbance, turbidity, fluorescence/luminescence, and optical scattering measurements. Optical laser scattering is one of the most sensitive methods, but its implementation can be very challenging, especially when analyzing biological samples in which suspended particles are relatively transparent in the medium.
One particle that often requires evaluation within a liquid is bacteria. The presence of bacteria is often checked with biological liquids, such as urine, amniotic, pleural, peritoneal and spinal liquids. In a common analytical method, culturing of the bacteria can be time-consuming and involve the use of bacterial-growth plates placed within incubators. Normally, laboratory results take several days to determine whether the subject liquid is infected with bacteria.
In some optical measurement systems, cuvettes have been used to receive liquid samples that are then subjected to the optical measurement by transmission of an input beam through the cuvette and observation of the forward scatter signals. These devices have been used relative to the detection of bacteria within the liquid. To optically measure the bacteria, it is often necessary to filter the fluid from other particles. In use, the cuvette is often filled by a pipette assembly that contains the liquid sample. However, filtering the fluid sample prior to transfer to the cuvette or within the cuvette can often be difficult.
Some clinical and research activities involve testing of large numbers of samples, and a variety of semi-standardized air displacement pipetting devices have been developed to simplify transfer of samples between containers while avoiding contamination. These generally involve pulling some volume of air from a disposable pipette tip using a manually actuated cylinder, and pulling liquid into the tip by the vacuum created, and then releasing the sample by moving the cylinder back to the original position, venting the tip to ambient pressure, or by applying an overpressure by use of the same cylinder.
Filtration is used to remove particles of a range of sizes from liquids, and for some medical and lab activities it is common to use a syringe and syringe filter device, which are commonly available. In this arrangement the liquid is drawn into the syringe volume, a filter is attached to the syringe luer fitting, and then the sample is pressed through the filter. This activity requires the assembly of the filter on the syringe after the syringe has been loaded with the sample and thereby exposed to the sample, which might include pathogenic organisms, and is therefore prone to unintended spills, drips, or cross-contamination. Additionally, since the syringe plunger is directly contacting the incompressible sample liquid, it is possible to apply extremely high pressure to the sample, which can crack the filter body leading to spills.
Accordingly, there is a need for an improved pipette assembly with an integrated filter to permit the fluid sample to be easily pulled into the pipette and filtered prior to dispensing the fluid sample.